While the global efforts of earth environment preservation proceed, intensification of regulations regarding exhaust gas or fuel efficiency in internal combustion engines, such as engines of automobiles is under way. Turbochargers are rotary machines that can enhance effects of fuel efficiency improvement and CO2 reduction by sending compressed air into an engine to combust fuel compared to natural intake engines.
In the turbochargers, a turbine is rotationally driven with exhaust gas of an engine, thereby rotating an impeller of a centrifugal compressor. The air compressed by the rotation of the impeller is raised in pressure by being reduced in speed by a diffuser, and is supplied to the engine through a scroll flow passage. In addition, as methods for driving the turbochargers, not only methods of being driven with exhaust gas but also, for example, methods using electric motors, methods using prime movers, and the like are known.
As an impeller of a turbocharger, an impeller using a complex material (hereinafter referred to as a resin) of synthetic resins, such as carbon fiber reinforced plastic, is known as described in, for example, PTL 1. Here, such a resin impeller has low rigidity compared to a metallic impeller, and if the resin impeller rotates, the amount of deformation thereof becomes large under the influence of a centrifugal force. For this reason, a boss hole into which a rotating shaft is fitted may be increased in diameter, and rotation balance may be impaired.
In view of such a problem, in the impeller described in PTL 1, the deformation of the impeller by the centrifugal force is suppressed by providing a back surface part with a metallic ring.